The hepatitis C virus (HCV), a single-stranded RNA virus, is the etiological agent of blood-borne non-A, non-B hepatitis. Chronic active infection with HCV often progresses to liver cirrhosis and hepatocellular carcinoma. Epidemiological studies indicate that HCV infects more than 170 million people worldwide with a high incidence of chronic disease ultimately progressing (more than 50% of cases) to death. However, since it is mainly a blood-borne disease, it is possible to identify the pathogen in blood samples and to eliminate the transmission of disease through blood transfusion. After exposure to the HCV pathogen, there is initially no evidence of viral presence, i.e. no detectable viral RNA or serology markers. This is referred to as the “window period” (WP). Generally, after 10 days following exposure to HCV, viral RNA can be detected while anti-HCV antibodies become detectable approximately 70 days later (Busch MP and Dodd RY, Transfusion 40(10): 1157-1160, 2000). To prevent spread of HCV infection, it is extremely important to take this observable fact into consideration and to establish a reliable blood-screening test, which would narrow the detection window. Since the commercialization of the nucleic acid amplification testing (NAT) which detects HCV RNA, the post-transfusion HVC infection rate has been dramatically reduced. Other methods are based on serological screening of the blood for detecting the presence of HCV core antigen (Ortho HCV Core Antigen ELISA, Ortho-Clinical Diagnostics, Inc., Raritan, N.J.) or antibodies against HCV polypeptides (Ortho HCV 3.0 ELISA, Ortho-Clinical Diagnostics, Inc., Raritan, N.J.) in patient serum or plasma.
According to a survey conducted by Seme et al. (J. Clin. Virol. 32(2): 92-101, 2005), the first generation HCV core antigen assay detects HCV infection with comparable sensitivity and detection limits to the nucleic acid techniques (NAT). These assays detect HCV infection between 40 to 50 days earlier than the current third generation HCV antibody screening assays. Although the first generation HCV core antigen assay, designed for blood screening, has significantly reduced the window period, it only detects core antigen at pre-seroconversion or early post-seroconversion phase. Furthermore, the first generation HCV core antigen assay is unable to detect core antigen when the antigen forms immune-complexes with anti-core antibodies in the late seroconversion phase. Clearly, it is desirable to have a combined serology assay that can detect HCV core antigen in the pre-seroconversion phase as well as anti-HCV antibodies in the seroconversion phase, thus narrowing the WP significantly. This combined serology test can especially be a valuable method of blood screening in settings where the NAT test can not be carried out due to lack of equipment or competency.
Such an HCV antigen and antibody combined assay will be a significant improvement over the current third generation serology blood screening method (Ortho HCV 3.0 ELISA, Ortho-Clinical Diagnostics, Inc., Raritan, N.J.) with regards to narrowing the WP. However, one of the challenges to the successful antigen antibody combined assay is to select an appropriate detergent to disrupt HCV virions and release antigen without interfering with the capture of anti-HCV antibodies by recombinant HCV antigens.